1. Field of Invention
The present invention relates to wireless communications and, more particularly, to a method and an apparatus for determining the number of sub-rate channels needed for a backhaul link based on variations in the coding schemes used at the wireless system air interface.
2. Description of Related Art
In Global System For Mobile Communications (GSM) systems, a busy air interface timeslot occupies one sub-rate channel on the wired backhaul link (i.e., the Abis link), which is the link between the base station transceiver (BST) and the base station controller (BSC). This is not true for General Packet Radio Service (GPRS) and Enhanced Data GSM Environment (EDGE) systems. In GSM and EDGE systems, each air interface timeslot may require up to four sub-rate channels on the Abis link. The number of sub-rate channels required depends on the vendor's coding scheme selection algorithm. The data rate at the air interface varies with the coding scheme used because of the inverse relationship between the number of bits used for coding and the number of bits that can be included in the payload. Vendors often attempt to maximize the over-the-air data throughput of the wireless system by selecting the coding algorithm in accordance with changing conditions of the air interface. Fewer bits are used to encode the data during conditions of low interference than are used to encode the data during conditions of high interference.
The Abis link normally is provisioned by simply acquiring enough resources to support the worst case scenario. For example, because as many as four sub-rate channels could be required on the Abis link for each time slot of the air interface of an EDGE system, the number of sub-rate channels normally provisioned for the Abis link of an EDGE system is four. This type of provisioning method has obvious shortcomings. One major disadvantage of this provisioning method is that it often results more resources (e.g., T1 lines) being provisioned for the Abis link than is necessary.
A need exists for a backhaul provisioning technique that makes it possible to accurately determine the amount of resources that needs to be provisioned for the backhaul link.